Thin Wall Molding

Thin wall molding (high-speed injection molding) produces lightweight plastic parts with very thin sections using fast injection and robust tooling at high volumes.

Overview

Thin wall molding is a specialized injection molding process tuned for very thin nominal walls, high flow length-to-thickness ratios, and short cycle times. It relies on high injection speed/pressure, high clamp force, stiff tooling, and tightly controlled processing to fill before freeze-off and maintain dimensional stability.

Choose it for high-volume, weight-sensitive parts where cost-per-part matters and you can design for uniform thin walls. Typical strengths are rapid cycles, reduced resin usage, and high repeatability once the process window is locked.

Tradeoffs: tooling and presses are more demanding (higher upfront cost), material selection is narrower, and designs are less forgiving—small changes in gate location, venting, or wall transitions can drive short shots, warp, or burn. Expect more DFM iteration and process validation than standard molding, especially for large projected area parts or parts with long flow paths.

Common Materials

  • Polypropylene (PP)
  • High Impact Polystyrene (HIPS)
  • ABS
  • Polyethylene (HDPE)
  • Polycarbonate (PC)
  • PET

Tolerances

±0.003" to ±0.005"

Applications

  • Food container lids and tubs
  • Disposable cutlery and cups
  • Medical device housings and covers
  • Electronics battery covers and bezels
  • Cosmetic caps and closures
  • Thin-wall packaging trays

When to Choose Thin Wall Molding

Choose thin wall molding for high-volume production of lightweight parts with thin, uniform walls and long flow paths where cycle time and resin reduction drive unit cost. It fits best when you can commit to robust tooling, process development, and stable materials to hold a tight process window.

vs Standard Injection Molding

Choose thin wall molding when your design pushes wall thickness and flow length to the point where standard fill speeds risk freeze-off, sinks, or inconsistent packing. The higher-speed process and tooling approach is justified when cycle time and resin savings offset higher tool and press requirements.

vs Overmolding

Choose thin wall molding when the part is a single-material thin shell and you need minimum mass and fast cycles. If your design needs a second material for grip, sealing, or insulation, overmolding becomes the driver, but it typically increases tooling complexity and cycle time versus a thin-wall single shot.

vs Insert Molding

Choose thin wall molding when you don’t need embedded metal/plastic inserts and the main challenge is filling thin sections reliably. If electrical contacts, threaded bushings, or reinforcement inserts are required, insert molding is the better fit, but it adds handling/fixturing and can constrain flow and venting in thin sections.

vs Compression Molding

Choose thin wall molding for thin, detailed parts requiring good cosmetic surfaces and tight control of wall sections at high volumes. Compression molding is better aligned to thicker sections and certain thermosets; it typically won’t match thin-wall fill capability or cycle time for packaging-style geometries.

vs Blow Molding

Choose thin wall molding when you need precise features like snaps, ribs, bosses, or tight parting-line control on a thin shell. Blow molding is optimized for hollow containers and handles large enclosed volumes well, but it can’t deliver the same level of detailed functional geometry.

Design Considerations

  • Hold wall thickness as uniform as possible and avoid abrupt thick-to-thin transitions that freeze off and warp
  • Keep flow length-to-thickness realistic by adding gates or moving gates closer to thin extremities
  • Design generous radii at corners and rib bases to reduce pressure loss and shear heating
  • Vent aggressively at end-of-fill and around thin features to prevent burns and short shots
  • Minimize tall ribs, deep textures, and sharp shutoffs that can cause steel deflection and flash at high pressures
  • Specify material, color, target wall, and allowable warp early; thin-wall parts are process-window sensitive and need clear acceptance criteria